From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 26B0FC4361B for ; Thu, 10 Dec 2020 16:40:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DD9AB23D39 for ; Thu, 10 Dec 2020 16:40:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391944AbgLJQkj (ORCPT ); Thu, 10 Dec 2020 11:40:39 -0500 Received: from foss.arm.com ([217.140.110.172]:52484 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730173AbgLJQkE (ORCPT ); Thu, 10 Dec 2020 11:40:04 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CCFBD1396; Thu, 10 Dec 2020 08:39:18 -0800 (PST) Received: from e113632-lin.cambridge.arm.com (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 7E86D3F66B; Thu, 10 Dec 2020 08:39:16 -0800 (PST) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: Qian Cai , Peter Zijlstra , tglx@linutronix.de, mingo@kernel.org, bigeasy@linutronix.de, qais.yousef@arm.com, swood@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vincent.donnefort@arm.com, tj@kernel.org, ouwen210@hotmail.com Subject: [PATCH 2/2] workqueue: Fix affinity of kworkers attached during late hotplug Date: Thu, 10 Dec 2020 16:38:30 +0000 Message-Id: <20201210163830.21514-3-valentin.schneider@arm.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20201210163830.21514-1-valentin.schneider@arm.com> References: <20201210163830.21514-1-valentin.schneider@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Per-CPU kworkers forcefully migrated away by hotplug via workqueue_offline_cpu() can end up spawning more kworkers via manage_workers() -> maybe_create_worker() Workers created at this point will be bound using pool->attrs->cpumask which in this case is wrong, as the hotplug state machine already migrated all pinned kworkers away from this CPU. This ends up triggering the BUG_ON condition is sched_cpu_dying() (i.e. there's a kworker enqueued on the dying rq). Special-case workers being attached to DISASSOCIATED pools and bind them to cpu_active_mask, mimicking them being present when workqueue_offline_cpu() was invoked. Link: https://lore.kernel.org/r/ff62e3ee994efb3620177bf7b19fab16f4866845.camel@redhat.com Fixes: 06249738a41a ("workqueue: Manually break affinity on hotplug") Reported-by: Qian Cai Signed-off-by: Valentin Schneider --- kernel/workqueue.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 9880b6c0e272..fb1418edf85c 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1848,19 +1848,29 @@ static void worker_attach_to_pool(struct worker *worker, { mutex_lock(&wq_pool_attach_mutex); - /* - * set_cpus_allowed_ptr() will fail if the cpumask doesn't have any - * online CPUs. It'll be re-applied when any of the CPUs come up. - */ - set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask); - /* * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains * stable across this function. See the comments above the flag * definition for details. + * + * Worker might get attached to a pool *after* workqueue_offline_cpu() + * was run - e.g. created by manage_workers() from a kworker which was + * forcefully moved away by hotplug. Kworkers created from this point on + * need to have their affinity changed as if they were present during + * workqueue_offline_cpu(). + * + * This will be resolved in rebind_workers(). */ - if (pool->flags & POOL_DISASSOCIATED) + if (pool->flags & POOL_DISASSOCIATED) { worker->flags |= WORKER_UNBOUND; + set_cpus_allowed_ptr(worker->task, cpu_active_mask); + } else { + /* + * set_cpus_allowed_ptr() will fail if the cpumask doesn't have any + * online CPUs. It'll be re-applied when any of the CPUs come up. + */ + set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask); + } list_add_tail(&worker->node, &pool->workers); worker->pool = pool; -- 2.27.0